1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and methods for generating a downhole overpull force. More specifically, the present invention relates to jarring with a downhole overpull generator.
2. Description of the Related Art
In a conventional downhole fishing operation, a bottom hole assembly is lowered into a wellbore on a drill string. The bottom hole assembly typically includes a slinger, a jar, and a fishing tool (such as an overshot) that are connected via drill collars and drill pipe. A jar is a device that is used downhole to deliver an impact load to another downhole component, especially when that object is stuck in the wellbore. The jar generally includes a device for storing energy (e.g. a spring or a pressure chamber) and a triggering device that is configured to activate the jar at a predetermined instant, thereby allowing the jar to deliver the impact load.
During the fishing operation, the bottom hole assembly is lowered into the wellbore and attached to the object stuck in the wellbore by utilizing the fishing tool. Thereafter, a rig at the surface of the wellbore is used to pull up on the drill string, imparting a force on the drill string and storing the created energy in the slinger and the drill string. At a predetermined pull force and/or time, the triggering device in the jar activates the jar, thereby causing the jar to deliver the impact load to the object stuck in the wellbore.
The use of a bottom hole assembly in a conventional fishing operation may be effective in dislodging an object stuck in a vertical wellbore since the rig is able to pull up on the drill string and generate the energy for use with the jar. However, a problem arises when the same bottom hole assembly is used in a deviated wellbore. In this situation, the rig is not fully pulling up on the drill string and generating the energy for use with the jar due to the curvature and the associated friction between the drill string and the wall of the wellbore.
Therefore, there is a need for a device and a method of generating a overpull force downhole. There is a further need for a device and a method of fishing with a downhole overpull generator.